An insulating contact holder (26) is reciprocally movable in sliding engagement between flexible stationary contacts (22, 24) to interrupt the circuit therebetween in one position of the holder and to carry a contact (32) into bridging engagement with said stationary contacts in another position of the holder. A wedge formation (40) on the holder separates the stationary contacts a predetermined distance in the circuit interrupting position, and movement therefrom to the bridging position causes said stationary contacts (22, 24) to converge immediately prior to engagement by the bridging contact (32), thereby to relieve the bias in the stationary contacts prior to said bridging engagement to reduce contact bounce. The wedge surfaces (42) are provided with a matte surface for cleaning the stationary contacts.